What does ADHD look like in the brain of a preschooler?

According to the National Survey of Children’s Health from 2016, 9.4% of children in the United States have been diagnosed with ADHD, almost 1 in 10 children. ADHD, or attention-deficit/hyperactivity disorder, is a neurological disorder characterized by impulsive behavior, different attention patterns, restlessness, and disorganization. You might hear a coworker casually claim, “I can’t focus on these emails.. my ADHD is acting up!” However, ADHD is not something that comes and goes. It is a different way of thinking, which stems from abnormal brain developmental patterns.

Although ADHD can manifest as early as 4 years old, most studies have only analyzed older school-age children. A new study published online in March 2018 in the Journal of the International Neuropsychological Society recruited a group of 4-5 year olds, including 52 children exhibiting ADHD symptoms and 38 children without ADHD symptoms to use as a comparison group. With consent from both the parents and children of course, they performed MRI scans to get a look at their brain structure.

Overall, the researchers found that some regions of the brain had a smaller volume in children with ADHD, compared to the group of children with no ADHD symptoms. In particular, gray matter volumes were decreased. Gray matter, named for its natural brownish-gray color, is tissue comprised of the cell bodies of neurons in the brain and spinal cord. A neuron cell has a central body, and a long axon “branch” which sends messages to other neurons. The neuron cell bodies tend to congregate together in the brain and arrange themselves as “gray matter.” The axons also form groupings and are visualized as white matter.

In the brains of children with ADHD, the researchers noticed that the gray matter volume was reduced most significantly in subregions of the right frontal lobe and the left temporal lobe of the brain, and greater losses in volume corresponded with greater severity of ADHD symptoms. These brain areas with smaller gray matter volume are involved in inhibitory control (for example, preventing one’s self from blurting out an answer instead of raising a hand in class), working memory (for example, remembering the question on a worksheet while in the middle of writing an answer), planning (for example, deciding to clean up the desk, then turn in homework, then put books in backpack in that order), and response control (for example, correctly following a teacher’s directions).

A schematic of the brain showcasing the frontal lobe and temporal lobe, each of which play a role in ADHD symptoms; Credit: w:User:Washington irving, Wikipedia Commons.

Previously, gray matter volume differences have been assessed in older children, but this study demonstrates that brain structure developments are discernible in children as young as four. The gray matter volume of another brain area, the anterior cingulate cortex, which plays a role in attention, decision-making, and impulsivity, has been evaluated in other studies. In older children with ADHD, there is a reduction in volume of the anterior cingulate cortex, but there was no difference between groups in the 4-5 year olds, suggesting that neural development is transpiring during the course of several years.

Scientists are gaining a better understanding of developmental trajectories of ADHD with this kind of research. The hope is that these research studies will one day shed light on what triggers the differences in gray matter volume. These neurological differences are believed to be shared by Albert Einstein, Walt Disney, and John F. Kennedy, who also had ADHD symptoms. With this knowledge, we can gain a greater appreciation of what makes us who we are.

Sources:

Children and Adults with Attention-Deficit/Hyperactivity Disorder (CHADD). (2018). General Prevalence. CHADD: The National Resource on ADHD. Retrieved Apr 3, 2018 from http://www.chadd.org/Understanding-ADHD/About-ADHD/Data-and-Statistics/General-Prevalence.aspx.